Liberty Media Corp., the holding company controlled by billionaire cable magnate John Malone, has offered to buy the 48 percent of Sirius XM Holdings it doesn’t already own in a roughly $10 billion all-stock deal that values the satellite radio company at $27 billion.

A late Friday SEC filing by Liberty Media shows it has retained Baker Botts as outside counsel on the proposed transaction, which would see Sirius XM become a wholly owned subsidiary of Malone’s media giant.